Don't forget to get a serviceable centering ball too. Many have had serviceable U-joints only to have the grease in the centering ball fail and blow up the shaft.
You can rebuild it, but everything must be serviceable.
Likewise, you can read posts about people who would service their U-joints but fail to grease the centering ball (requires a Lincoln needle-point fitting), with the same result.
It's not a big deal if you can keep up with it, and if you line up all your zirc/ball fittings you can grease the whole thing in one shot. I've heard you need to lift up the front, but with my 2" OME lift, I can grease it all from the ground.